AoC 2023.1 p1+2

1 files changed, 84 insertions, 0 deletions

diff --git a/trebuchet/t.scm b/trebuchet/t.scm
new file mode 100644
index 0000000..8bc7385
--- /dev/null
+++ b/trebuchet/t.scm
@@ -0,0 +1,84 @@
+(define-module (t)
+  #:use-module (srfi srfi-1)
+  #:export (t
+	    spelt->numbers
+	    starts-with?
+	    parse-int
+	    replace-elements
+	    find-true))
+
+
+(define numbers '((#\1 . ((#\o #\n #\e) . 3))
+		  (#\2 . ((#\t #\w #\o) . 3))
+		  (#\3 . ((#\t #\h #\r #\e #\e) . 5))
+		  (#\4 . ((#\f #\o #\u #\r) . 4))
+		  (#\5 . ((#\f #\i #\v #\e) . 4))
+		  (#\6 . ((#\s #\i #\x) . 3))
+		  (#\7 . ((#\s #\e #\v #\e #\n) . 5))
+		  (#\8 . ((#\e #\i #\g #\h #\t) . 5))
+		  (#\9 . ((#\n #\i #\n #\e) . 4))))
+
+
+(define (t str convert?)
+  (apply + (map (lambda (line)
+		  (let ((lst (string->list line)))
+		    (parse-int
+		     (if convert?
+			 (spelt->numbers lst)
+			 lst))))
+		(string-split
+		 (string-trim-both str char-set:whitespace)
+		 #\newline))))
+
+(define (parse-int lst)
+  "Given LST of characters, return a
+two-digit integer representing containing
+the first and last digits in LST."
+  (let ((digits (filter (lambda (x) (char-numeric? x))
+			lst)))
+    (string->number
+     (string (car digits)
+	     (last digits)))))
+
+(define (spelt->numbers lst)
+  "Loops through the string, replacing
+numbers that are spelt-out with their
+digit counterparts."
+  (let loop ((lst lst) (result '()))
+    (if (null? lst)
+	result
+	(let ((index
+	       (find-true
+		(map (lambda (num-pair)
+		       (starts-with? lst num-pair))
+		     numbers))))
+	  (when index
+	    (set! lst (replace-elements lst (list-ref numbers index))))
+	  (loop (cdr lst)
+		(append result (list (car lst))))))))
+
+(define (find-true lst)
+  "Given LST of boolean values,
+returns the index of the first #t value,
+or false otherwise."
+  (let ((sublist (member #t lst)))
+    (if sublist
+        (- (length lst) (length sublist))
+        #f)))
+
+(define (starts-with? lst num-pair)
+  "Returns #t if LST starts with CADR
+NUM-PAIR"
+  (let ((sub-length (cddr num-pair)))
+    (and (>= (length lst) sub-length)
+	 (equal? (list-head lst sub-length) (cadr num-pair)))))
+
+(define (replace-elements lst num-pair)
+  "Given LST, removes LENGTH elements from
+the front and replaces them with CHAR.
+
+As an edit, we should NOT remove ALL letters,
+because some letters are shared between
+spelt numbers (twone). As a safety, we are
+safe always leaving one."
+  (cons (car num-pair) (list-tail lst (1- (cddr num-pair)))))